Time-Ordered Event Traces: A New Debugging Primitive for Concurrency Bugs

Non-determinism makes concurrent bugs extremely difficult to reproduce and to debug. In this paper, the authors propose a new debugging primitive to facilitate the debugging process by exposing this non-deterministic behavior to the programmer. The key idea is to generate a time-ordered trace of events such as function calls/returns and memory accesses across different threads. The architectural support for this primitive is lightweight, including a high-precision, frequency-invariant time-stamp counter and an event trace buffer in each processor core. The proposed primitive continuously records and timestamps the last N function calls/returns per core by default, and can also be configured to watch specific memory addresses or code regions through a flexible software interface.